Laser welding method

ABSTRACT

A laser welding method allowing lap welding with a mother member and an attaching member overlapping each other, without incurring a lowering of strength. In laser welding, a laser beam is directed to a flange ( 4 ) along a welding path ( 16 ) extending from a welding start point ( 12 ) to a welding termination point ( 14 ). Further, the welding path ( 16 ) is turned back before reaching the welding termination point ( 14 ), and the welding termination point ( 14 ) is located at a place where there is no stress concentration due to external forces on the mother member ( 1 ) and the attaching member ( 2 ) without coincidence between the welding start point ( 12 ) and the welding termination point ( 14 ). The welding path ( 16 ) is substantially C-shaped, and, after it is turned back, a longer welding path than the crater produced in the welding termination point ( 14 ) is provided to complete the welding termination point ( 14 ).

TECHNICAL FIELD

This invention relates to a laser welding method for welding anattaching member to a mother member, more particularly to a laserwelding method for motor vehicles, in which a pipe for reinforcement, towhich an instrument panel, etc. is attached, and an attaching member,are welded together.

BACKGROUND ART

Heretofore, a laser welding method has been adopted when a mother memberand an attaching member are lap welded. For example, as shown in FIG.4A, when a mother member 100, which is a pipe, and an attaching member102 are welded together, a flange part 104 having a shape of a circulararc, adapted to a shape of an outer periphery of the mother member 100,is formed to the attaching member 102. A laser beam is directed to theflange part 104 along a welding path 110 extending from a welding startpoint 106 to a welding termination point 108 to accomplish lap welding.

However, in laser welding, welding is performed melting the mothermember without using a welding rod. Therefore, in such a conventionalmethod, when a welded part immediately before the welding terminationpoint is getting hardened, a melted portion of the mother member at thewelding termination point is pulled by the welded part. As a result, acrater 112 is formed as shown in FIG. 4B.

Due to the crater 112, fatigue strength is lowered at the weldingtermination point 108. Accordingly, if external forces are appliedbetween the mother member 100 and the attaching member 102, the crater112 may become a cause of damage in an extreme case.

One object of the present invention is to provide a laser welding methodthat allows lap welding of a mother member and an attaching member,without incurring a lowering of strength.

DISCLOSURE OF THE INVENTION

To attain the above object and solve the aforementioned problem, thepresent invention provides a laser welding method as follows. In awelding method in which a flange part of an attaching member is arrangedonto a mother member and welded to the same, the welding corresponds tolaser welding, and a laser beam is directed to the flange part along awelding path extending from a welding start point to a weldingtermination point to perform welding. The welding path is turned backbefore reaching the welding termination point, without overlap betweenthe welding start point and the welding termination point. The weldingtermination point is located at a place where there is no stressconcentration due to external forces on the mother member and theattaching member.

The welding path may be substantially C-shaped, and after the weldingpath is turned back, a longer welding path than a crater produced in thewelding termination point may be provided to complete the weldingtermination point. Or, the welding path may be spiral-shaped includingat least one round which extends from an outer welding start point to aninner welding termination point, and after the welding path makes oneround, a longer welding path than the crater produced in the weldingtermination point may be further provided to complete the weldingtermination point. The mother member may be a pipe, and the flange partmay be formed into a circular arc, adapted to a shape of an outerperiphery of the pipe. The mother member and the attaching member may befor use in reinforcement of an instrument panel of a motor vehicle. Thelaser welding may be remote laser welding in which a long-focus laserbeam is reflected in a mirror and guided along the welding path.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic perspective view showing a laser welding methodas an embodiment of the present invention;

FIG. 2 is an explanatory view of remote laser welding according to theembodiment;

FIGS. 3A and 3B are explanatory views of a welding path according to theembodiment; and

FIGS. 4A and 4B are diagrammatic perspective views showing conventionalwelding.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be explained hereafter, byway of the accompanying drawings.

As shown in FIG. 1, a mother member 1 in the present embodiment is apipe, having a diameter of 38.1 mm and a thickness of 1.0 mm. The pipeis used as a reinforcement to which an instrument panel, etc. of a motorvehicle is attached. An attaching member 2 welded to the mother member 1is provided with a flange part 4, which is formed into a circular arc,adapted to a shape of a curved surface of an outer periphery of themother member 1.

In the present embodiment, the attaching member 2 has a thickness of 1.6mm, which is larger than a thickness of the mother member 1. The flangepart 4 is bent by press molding, etc., so that the flange part 4 can bearranged onto the outer periphery of the mother member 1 in a closelyattached manner.

Remote laser welding is applied to the present embodiment. As shown inFIG. 2, from a welding laser oscillator 6, a long-focus laser beam 8having a focal length of 600 to 1,000 mm is emitted. The laser beam 8irradiated in a mirror 10 is guided to the flange part 4.

An angle of the mirror 10 is capable of being changed. By changing theangle, a guiding direction of the laser beam 8 can be shifted along acircumferential direction and an axial direction of the mother member 1.Accordingly, an irradiation point of the laser beam 8 is capable ofbeing displaced on a plane surface. However, in case the laser beam 8 isguided to the curved surface of the pipe having a diameter of 38.1 mm asin the present embodiment, if an irradiation angle of the laser beam 8exceeds 20 degrees, diffusion of energy becomes large and welding can nolonger be performed. In the present embodiment, on the curved surface ofthe pipe having a diameter of 38.1 mm, the maximum welding length in thecircumferential direction is limited to about 15 mm.

In the present embodiment, as shown in FIG. 3A, the welding path 16extending from the welding start point 12 to the welding terminationpoint 14 is looped, and the welding start point 12 and the weldingtermination point 14 do not overlap with each other so that the weldingpath 16 is substantially C-shaped. The reason for avoiding overlapbetween the welding start point 12 and the welding termination point 14is because, if there is such overlap, a hole may be produced by melting.

The laser welding starts from the welding start point 12 of the weldingpath 16. The welding path 16, which extends in the circumferentialdirection of the mother member 1 from the welding start point 12, turnsback in a semicircular arc turning part 16 a to head for an oppositedirection in the circumferential direction. After forming a linear part16 b having a predetermined length, the welding path 16 turns back againto an opposite direction in a semicircular arc turning part 16 c to forma linear part 16 d. The laser welding is completed at the weldingtermination point 14 which is spaced apart from the welding start point12 by a predetermined distance.

The welding termination point 14 is located at a place where there is nostress concentration due to external forces applied to the mother member1 and the attaching member 2. In the present embodiment, the externalforces are applied to the attaching member 2 as shown by an arrow inFIG. 1, and a moment around an axis of the mother member 1 is generated.

Consequently, the stress concentrates on both of the semicircular arcturning parts 16 a and 16 c of the welding path 16. On one hand, atensile force, which operates to tear off the turning part 16 c from themother member 1, acts on the attaching member 2 with the turning part 16a serving as a fulcrum. On the other hand, a tensile force, whichoperates to tear off the turning part 16 a from the mother member 1,acts on the attaching member 2 with the turning part 16 c serving as afulcrum. The above tensile forces repeatedly act by turns.

In the present embodiment, the welding termination point 14 is notprovided in the turning part 16 c. The linear part 16 d is furtherprovided, which extends from the turning part 16 c and is longer than acrater produced in the welding termination point 14, to complete thewelding termination point 14. Therefore, the stress concentration doesnot occur at the welding termination point 14. That is, even if theexternal forces are repeatedly applied between the mother member 1 andthe attaching member 2, the external forces act on the turning parts 16a and 16 c where appropriate welding has been performed. Thus, themother member 1 and the attaching member 2 can be lap welded withoutincurring a lowering of fatigue strength.

A length of the crater varies depending on material quality and weldingconditions of the mother member 1 and the attaching member 2. Therefore,it is preferable that a length of the linear part 16 d is determined byex ante experiments. Also, the turning parts 16 a and 16 b may not beformed into a circular arc but a rectangular shape. Or the welding path16 may be an elliptic arc which includes the turning parts 16 a and 16 cand the linear parts 16 b and 16 d.

The welding path 16 may not be substantially C-shaped. As shown in FIG.3B, a spiral-shaped welding path 18 is also acceptable. The welding path18 extends from an outward welding start point 20 to an inward weldingtermination point 22.

Starting from the welding start point 20, the welding path 18 turns backat a semicircular arc turning part 18 a to extend toward an oppositedirection in the circumferential direction. After forming a linear part18 b having a predetermined length, the welding path 18 turns back at asemicircular arc turning part 18 c to form a linear part 18 d extendingto an opposite direction. After forming the linear part 18 d, thewelding path 18 turns back at a semicircular arc turning part 18 e toform a turning part 18 e inward of the welding start point 20.

After forming the turning part 18 e, a linear part 18 f is providedwhich is longer than a crater produced in the welding termination point22, to complete the welding termination point 22. As a result, thewelding path 18, after making one round, is provided with a linear part18 f which is longer than the crater produced in the welding terminationpoint 22.

Therefore, stress concentration does not occur at the weldingtermination point 22. That is, even if external forces are repeatedlyapplied between the mother member 1 and the attaching member 2, theexternal forces act on the turning parts 18 a and 18 c where appropriatewelding has been performed. Thus, the mother member 1 and the attachingmember 2 can be lap welded without incurring a lowering of fatiguestrength.

The welding termination point 22 may be located in the turning part 18e, as far as the turning part 18 e has a length relative to the lengthof the crater produced at the welding termination point 22, and thewelding path 18 having at least one round is formed so that the weldingtermination point 22 is located at a position inward of thespiral-shaped welding path 18 from the welding start point 20.

The linear parts 18 b, 18 d and 18 f are not necessarily provided in thewelding path 18. The welding path 18 may only consist of the circulararc turning parts 18 a, 18 c and 18 e, and the welding termination point22 may be provided in the turning part 18 e. Or, the linear parts 18 b,18 d, and 18 f may also be formed into a circular arc so that thewelding path 18 is shaped like an ellipse.

The present invention is not limited to the above embodiment, and othermodifications and variations may be possible without departing from thespirit and scope of the present invention.

INDUSTRIAL AVAILABILITY

According to the above-described laser welding method of the presentinvention, the mother member and the attaching material can be lapwelded without incurring a lowering of strength. The present inventionis suitable for welding an attaching member to a pipe for reinforcement,to which an instrument panel, etc. of a motor vehicle is attached.

1. A welding method for arranging a flange part of an attaching memberonto a mother member and welding the flange part to the mother member,in which the welding corresponds to laser welding, and a laser beam isdirected to the flange part along a welding path extending from awelding start point to a welding termination point to perform welding,the welding path being turned back before reaching the weldingtermination point, without overlap between the welding start point andthe welding termination point, and the welding termination point beinglocated at a place where no stress concentration occurs due to externalforces on the mother member and the attaching member.
 2. The laserwelding method according to claim 1, wherein the welding path issubstantially C-shaped, and after the welding path is turned back, alonger welding path than a crater produced in the welding terminationpoint is provided to complete the welding termination point.
 3. Thelaser welding method according claim 1, wherein the welding path isspiral-shaped, having at least one round which extends from an outerwelding start point to an inner welding termination point, and after thewelding path makes the one round, a longer welding path than a craterproduced in the welding termination point may be further provided tocomplete the welding termination point.
 4. The laser welding methodaccording to one of claims 1 to 3, wherein the mother member is a pipe,and the flange part is formed into a circular arc, adapted to a shape ofan outer periphery of the pipe.
 5. The laser welding method according toone of claims 1 to 4, wherein the mother member and the attaching membermay be for use in reinforcement of an instrument panel of a motorvehicle.
 6. The laser welding method according to one of claims 1 to 5,wherein the laser welding corresponds to remote laser welding in which along-focus laser beam is reflected in a mirror and guided along thewelding path.